One place to start is here: http://astronautix.com/lvs/atlasv.htm
You also might want to check the photo archives at spaceflightnow.com; that site has some good roll-out and launch photos. I don't know if they show every detail you want, but it's a place to look.
There's not a lot of detail down there as it is. If you go here spaceflightnow.com/atlas/ac204 and scroll down, you'll find an in-flight photo of the underside of the vehicle. If you spend the money and become a "Spaceflight Now+Plus" subscriber, you can view videos of Atlas 3 pre-launch processing which would probably show you what you needed. And lots of other stuff, too.
Before the Atlas 3 was discontinued, there were some good diagrams and photos of the vehicle's components (including the thrust structure) in the Mission Planners Guide, which can be found on the Lockheed-Martin website. I downloaded it and used to have a copy on my desktop, but I don't have it anymore. I may have some photos and diagrams that I printed from it sitting in a file at home; I'll check tonight. I had done a bunch of research on the Atlas 3 because I scratchbuilt a 1/96th-scale card version of it.
For what it's worth, you can find the current version of the MPG on the company's website, but it just covers the Atlas 5. You could perhaps e-mail Lockheed-Martin and/or ULA and ask them if they have an old version of the MPG in electronic form that they can send you.